In Fig. 6.12, PQ = PR, RS = RQ and ST ∥ QR. If the exterior angle RPU is 140°, then the measure of angle TSR is
(a) 55°
(b) 40°
(c) 50°
(d) 45°
Exterior ∠RPU = 140°. Interior ∠P = 40°. Isosceles gives base angles = 70°. So ∠TSR = 40°.